A United Airlines flight from Washington to Las Vegas was diverted to Denver on Saturday night after a passenger became unruly and tried to open a cabin door, authorities said.

Other passengers subdued the man and he was removed from the airplane at the Denver airport, authorities said. The man, who was not identified immediately, was being questioned by the FBI, a bureau spokesman said.

United Flight 223, an Airbus, was carrying 129 passengers and a crew of five when it left Dulles International Airport shortly after 5 p.m., an airline spokesman said. It landed safely at Denver about 6:45 p.m. Eastern time.

Barry Eynon of Coopersburg, Pa., said in a phone interview that he was in the third row when another passsenger "saw this person trying to open the airplane door and trying to get into the cockpit." The other passenger "jumped up and grabbed him from behind and yelled for help."

Eynon said, "I jumped up and grabbed him from the front."

Three or four other passengers also helped to subdue the man, putting him in a seat and ensuring he remained there, Eynon said.

Authorities in Denver said the attempt to open the door was unusual. "We don't hear that often," said Denver airport spokesman Jeff Green. Opening the door in the air is "pretty much impossible."